EP3433910B1 - Laserverstärkervorrichtung mit aktiver steuerung der strahlqualität - Google Patents

Laserverstärkervorrichtung mit aktiver steuerung der strahlqualität Download PDF

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Publication number
EP3433910B1
EP3433910B1 EP17711231.5A EP17711231A EP3433910B1 EP 3433910 B1 EP3433910 B1 EP 3433910B1 EP 17711231 A EP17711231 A EP 17711231A EP 3433910 B1 EP3433910 B1 EP 3433910B1
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Prior art keywords
amplifying
slab
plate
laser beam
amplified
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English (en)
French (fr)
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EP3433910A1 (de
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Alain Jolly
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Alphanov Centre Technologique Optique et Lasers
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
Alphanov Centre Technologique Optique et Lasers
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/042—Arrangements for thermal management for solid state lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/0405—Conductive cooling, e.g. by heat sinks or thermo-electric elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/0407—Liquid cooling, e.g. by water
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08072—Thermal lensing or thermally induced birefringence; Compensation thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
    • H01S3/10013—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by controlling the temperature of the active medium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/1301—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers
    • H01S3/13017—Stabilisation of laser output parameters, e.g. frequency or amplitude in optical amplifiers by controlling the temperature of the active medium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0606—Crystal lasers or glass lasers with polygonal cross-section, e.g. slab, prism
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0619—Coatings, e.g. AR, HR, passivation layer
    • H01S3/0625—Coatings on surfaces other than the end-faces
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/164—Solid materials characterised by a crystal matrix garnet
    • H01S3/1643—YAG
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2325—Multi-pass amplifiers, e.g. regenerative amplifiers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/23—Arrangements of two or more lasers not provided for in groups H01S3/02 - H01S3/22, e.g. tandem arrangements of separate active media
    • H01S3/2308—Amplifier arrangements, e.g. MOPA
    • H01S3/2325—Multi-pass amplifiers, e.g. regenerative amplifiers
    • H01S3/2333—Double-pass amplifiers

Definitions

  • the invention relates to the field of laser amplification devices, comprising an amplifying medium configured to amplify an incident laser beam, when it is optically pumped by one or more laser diodes or stacks of laser diodes.
  • the incident laser beam is called the laser beam to be amplified
  • the beam after amplification is called the amplified laser beam.
  • the invention relates more particularly to a laser amplification device offering active control of the beam quality, that is to say having active means for avoiding degrading the optical quality of the amplified laser beam.
  • the invention relates more particularly to a laser amplification device, in which the amplifying medium is in the form of a more or less thick plate (or “ slab ”, in English), called an amplifying plate.
  • the power of the beam of the pumping diodes must be confined inside the amplifying plate.
  • this intensity may have to be made greater than a predetermined threshold, called the transparency threshold, so that the pumping power must be very highly confined in a small volume.
  • This heating causes the appearance of temperature gradients, which develop inside the amplifying plate.
  • These temperature gradients result first of all in a non-homogeneous distribution of the values of the optical index of the amplifying plate, which harms the optical quality of the amplified laser beam.
  • These gradients are defined by a coefficient of variation of the optical index of the amplifying plate as a function of the temperature.
  • thermo-optical effect This first consequence of heating is called the thermo-optical effect.
  • thermo-mechanical effect This heating also causes the appearance of mechanical deformations at the faces of the amplifying plate, also contributing to degrading the wave surface of the amplified laser beam. This second consequence of heating is called thermo-mechanical effect.
  • the document US 6134258 illustrates an example of such a device, in which there is an amplifier plate 110, represented here in figure 1 , which comprises an entry face 111, for the entry of an incident laser beam, to be amplified, and an exit face 112, for the exit of said beam after crossing the plate, both inclined at the angle of Brewster.
  • an amplifier plate 110 represented here in figure 1 , which comprises an entry face 111, for the entry of an incident laser beam, to be amplified, and an exit face 112, for the exit of said beam after crossing the plate, both inclined at the angle of Brewster.
  • the document EP 1,492,207 shows a laser device, comprising an amplifier plate with a temperature control system (heating and cooling).
  • the incident laser beam 30, to be amplified propagates in a zigzag, by successive reflections on an upper face 113 and a lower face 114 of the amplifier plate (see dotted lines).
  • the upper and lower faces are each covered with a reflective coating.
  • the amplifier plate 110 is here pumped transversely, by pump beams 40 injected into the amplifier plate from a face 115 of the latter.
  • the amplifying plate 110 is cooled at its upper and lower faces, thanks to respective cooling elements 130A, 130B.
  • the two cooling elements 130A, 130B are identical.
  • Each cooling element 130A, 130B consists of a metal block, within which circulates a cooling liquid such as water, generally at room temperature (approximately 300 K).
  • These cooling elements improve the optical quality of the amplified laser beam, by reducing the average temperature in the amplifier plate.
  • this solution requires the use of an amplifying plate of reduced thickness, therefore offering a reduced section for the injection of the laser beam to be amplified, and then giving access only to low energy amplified laser pulses.
  • An objective of the present invention is to provide means for active control of the optical quality of an amplified laser beam, which can offer better control of the optical quality of the amplified laser beam than in the prior art.
  • Another object of the present invention is to provide means for active control of the optical quality of an amplified laser beam, making it possible to use an amplifying plate of increased thickness, for the same optical quality of the amplified laser beam.
  • an object of the present invention is to provide means for active control of the optical quality of an amplified laser beam, making it possible to use an amplifying plate with a thickness greater than 2 mm, such a thickness making it possible to generate High energy amplified laser pulses without significantly degrading the optical quality of the laser beam during amplification.
  • a laser amplification device comprising an amplifying plate having a lateral entry face and a lateral exit face for a laser beam to be amplified, and the upper and lower faces of which are each covered with a system.
  • the dependent claims define additional construction arrangements.
  • each temperature control system comprises a cooling element, covering a central region of the upper face, respectively lower of the amplifying plate, and at least one heating element, covering peripheral regions of the upper face. , respectively lower of the amplifier plate.
  • the temperature control systems according to the invention are substantially symmetrical to one another, according to an orthogonal symmetry with respect to a plane P passing through the amplifying plate.
  • the plane P is a plane parallel to the upper and lower faces of the amplifying plate.
  • Substantially symmetrical means that each temperature control system has a recovery rate of more than 90% with the symmetry of the other temperature control system, or even more than 95% or even 98%.
  • the two cooling elements make it possible to limit an overall heating of the amplifying plate.
  • the heating elements make it possible to obtain an increased optical quality of the amplified laser beam in the amplifying plate.
  • the heating elements make it possible in particular to act locally on the shape of the isothermal surfaces which develop inside the amplifying plate, in order to combat the harmful effects of the natural temperature gradients due to the necessary cooling of the amplifying plate.
  • This local action on the temperature gradients is implemented using symmetrical temperature control systems, which makes it possible to modulate a distribution of local temperatures inside the amplifying plate. , so as to limit a degradation in the quality of the wave surface of a laser beam at amplifier propagating in a straight line between the entry face and the exit face of the amplifying plate.
  • the beam after the crossing (s) in a straight line inside the amplifying plate forms the amplified laser beam.
  • the difference in optical path between two points of the wave surface of the amplified laser beam can be substantially zero, less than one tenth of the wavelength of said laser beam.
  • each point of the wave surface of a beam laser has traveled, after one or more crossings in a straight line inside the amplifier plate, a controlled value of optical path.
  • the optical path values associated with each point of the wave surface of the amplified laser beam together correspond to a known deformation of this wave surface, in particular a substantially cylindrical or spherical deformation.
  • the difference in optical path between two points of the wave surface of the amplified laser beam then corresponds to a substantially spherical, respectively cylindrical surface, comprised between two spherical, respectively cylindrical surfaces whose radii differ by less than a tenth of the length of said laser beam.
  • the deformation corresponds substantially to two cylindrical deformations along orthogonal axes.
  • the difference in optical path between two points of the wave surface of the amplified laser beam then corresponds to an aspherical surface, comprised between two aspherical surfaces each defined by two cylinders with orthogonal axes, the radii of the cylinders differing two by two by less than a tenth of the wavelength of said laser beam.
  • the invention therefore offers a new and inventive means for modulating the temperature gradients inside the amplifier plate, so that the beam can pass through said plate with minimal deformation of the incident wave surface. , thus giving access to better control of the optical quality of said laser beam after amplification, in comparison with the prior art.
  • An amplifying plate can be used all the thicker, as the degradation of the wave surface is greatly minimized.
  • a thick amplifier plate offers a large section for the injection of a laser beam to be amplified, making it possible to generate amplified laser pulses at very high energy and in a beam of high optical quality.
  • the at least one heating element advantageously extends at least along two opposite edges of the upper face, respectively lower, these opposite edges being located for one on the side of the lateral entry side and for the other side of the lateral exit side.
  • each temperature control system is substantially invariant by a rotation of 180 ° around an axis orthogonal to the upper face of the amplifier plate, each temperature control system having a recovery rate greater than 90%. with this same temperature control system rotated 180 ° around this axis.
  • the thickness of the amplifying plate can be greater than or equal to 3 mm.
  • the at least one heating element may have rounded faces, which extend facing the cooling element.
  • the at least one heating element may completely surround the cooling element.
  • the heating element may have a non-rectangular section, in a plane parallel to the upper face of the amplifying plate.
  • the device according to the invention further comprises at least one external lens which extends at the inlet, respectively at the outlet of the amplifying plate, configured to at least partially compensate for the effect of a thermo-mechanical deformation of the lateral faces. input and output of the amplifier plate.
  • the device according to the invention can also comprise two plane-cylinder external lenses, the axes of the cylinders being orthogonal to one another.
  • the cylinder axis of one of the plane-cylinder lenses may be parallel to the axis (Ox), and the axis of the other plane-cylinder lens parallel to the axis (Oy), where the lateral inlet and outlet faces mentioned above extend parallel to the plane (Oxy), in the absence of thermo-mechanical deformation.
  • the upper face, respectively lower face of the amplifying plate is covered directly by a layer called low index, of optical index lower than the average optical index of the amplifying plate, each low index layer being covered directly by the system corresponding temperature control.
  • the at least one heating element is supplied by adjustable supply means, and the adjustable supply means are connected to control means configured for formulate a control instruction as a function of a wave surface measurement and a maximum deformation instruction.
  • the device according to the invention may further comprise locating means relative to the amplifying plate, configured to guide the positioning of the laser beam to be amplified so that it propagates in a straight line in the amplifying plate.
  • the invention also relates to a system comprising a device according to the invention, as well as multiplexing means, configured to multiply a number of passages of the laser beam to be amplified, in the amplifying plate.
  • the multiplexing means are configured to implement a spatial multiplexing of the laser beam to be amplified, and comprise two reflectors arranged on the side of the input side face of the amplifying plate, and two reflectors arranged on the side of the side face of the amplifier plate.
  • the multiplexing means can be configured to also implement polarization multiplexing of the laser beam to be amplified, and also comprise a quarter wave plate and a reflector, configured to double a number of passages of the laser beam to be amplified in the plate amplifier.
  • the invention also covers a system comprising a laser amplification device according to the invention, and a source of emission of the laser beam to be amplified, configured so that the laser beam to be amplified propagates in a straight line in the amplifying plate, between its entry face and its exit face.
  • the system may include a laser amplification device according to the invention, and a housing configured to receive a source of emission of the laser beam to be amplified, and so that the laser beam to be amplified propagates in a straight line in the amplifier plate, between its entry face and its exit face.
  • the figure 2 illustrates a first embodiment of a laser amplification device 200 according to the invention, according to a perspective view.
  • the device 200 comprises an amplifying plate 210, forming an amplifying medium.
  • the amplifying plate 210 may consist of a crystal, a ceramic, or possibly a glass, doped for example by trivalent ions of rare earth.
  • the doping ion is for example the ytterbium Yb 3+ ion, typical of three-level laser media.
  • the neodymium doping ion Nd 3+ or any other element.
  • the amplifying plate forms an active medium at 4 levels.
  • the amplifying plate is made of Yb 3+ : YAG.
  • the amplifier plate here has the shape of a rectangular parallelepiped.
  • It has an entry side face, or entry face, for the entry of a laser beam to be amplified 300, an exit side face 212, or exit face, on the opposite side, for the exit of the laser beam to amplify.
  • the laser beam to be amplified can carry out several successive passages in the amplifying plate, and re-enter the amplifying plate by the so-called exit face, then exit again from the amplifying plate by the so-called face. Entrance.
  • the inlet and outlet faces 212 are parallel to each other, or substantially (to within a few degrees, for example to within +/- 2 °). They extend here in planes parallel to the plane (xy).
  • they are treated with high flux anti-reflection, at the wavelength of the laser beam to be amplified (around 1030 nm in the example considered of Yb 3+ : YAG).
  • the amplifying plate also includes an upper face and a lower face, each covered with a respective temperature control system, described below.
  • the upper and lower faces are parallel to each other, or substantially (to within a few degrees), and orthogonal to the inlet and outlet faces 212, or substantially (to within a few degrees, for example +/- 2 ° near). They extend here in planes parallel to the plane (yz).
  • the amplifying plate comprises two other opposite faces, called transverse faces, at least one of which forms a so-called pumping face, for the entry of a pump bundle 400.
  • the pump beam propagates here in the amplifying plate along an axis substantially orthogonal to this pumping face (within a few degrees), here along the axis (y).
  • the pump power is distributed almost uniformly over the entire volume of the amplifying plate.
  • the transverse face on the side opposite to the pumping face, is orthogonal to the inlet and outlet faces 212, and to the upper and lower faces. Here it extends in a plane parallel to the plane (xz).
  • This transverse face preferably, but not exclusively, has an anti-reflection treatment at the wavelength of the laser beam to be amplified, and, in the case of pumping by the only pumping face, a dichroic treatment for recycling the pump beam, of the reflector type at the pump wavelength (around 940 nm in the example considered of Yb 3+ : YAG).
  • a dichroic treatment for recycling the pump beam, of the reflector type at the pump wavelength around 940 nm in the example considered of Yb 3+ : YAG.
  • the pumping face can be slightly inclined relative to the plane (Oxz), to form an additional protection with regard to phenomena of amplified spontaneous emission.
  • the thickness E (along the axis (x)) of the amplifying plate 210 is advantageously equal to or greater than 3 mm, for example between 3 mm and 10 mm.
  • the width (along the axis (y)) of the plate is preferably between 20 and 50 mm.
  • the ratio between the width and the thickness of the amplifying plate is for example between 3 and 15, for example 10.
  • the dimensions of the amplifying plate are for example 5 mm thick, 10 mm long (along the axis (z)), and 25 mm wide.
  • This amplifier plate potentially offers an optical gain of between 15 and 20 dB, and makes it possible to amplify pulses of duration on the order of a nanosecond up to the 100 mJ range.
  • the description of the amplifying plate given above corresponds to its state at rest, in the absence of a thermomechanical deformation generated by the optical pumping of the laser beam to be amplified, and the possible phenomena of parasitic absorption.
  • the upper face of the amplifier plate is covered by a cooling element 231A, framed by two heating elements 232A, together forming a system 230A for controlling the spatial distribution of the temperature in the volume of the amplifier plate, hereinafter called , temperature control system.
  • the underside of the amplifier plate is covered by a cooling element 231B, framed by two heating elements 232B, together forming a temperature control system 230B.
  • each cooling element and each heating element extends along the entire width (axis (y)) of the amplifying plate, and its dimensions are invariant along this axis of the width.
  • the cooling elements 231A, 231B each consist of a metal block, pierced right through by a tunnel forming a flow circuit for a cooling liquid such as water.
  • the cooling elements 231A, 231B are known per se, one of the novelties residing in the fact that they each extend only over a reduced surface of the upper face, respectively lower of the amplifying plate.
  • Each cooling element 231A, respectively 231B, covers a so-called central region of the upper, respectively lower, face of the amplifying plate.
  • the region is said to be central because it extends midway between the input and output faces of the amplifier plate.
  • Each cooling element 231A, 231B is spaced from the corresponding heating elements 232A, 232B by a gap of approximately 1 mm.
  • each heating element is constituted by at least one heating electrode.
  • the heating element 232A, respectively 232B, is formed here by a respective heating electrode.
  • the heating electrodes 232A, 232B here cover more than half of the surface of the upper, respectively lower, face of the amplifying plate.
  • the heating electrodes 232A, respectively 232B cover peripheral regions of the upper, respectively lower, face of the amplifying plate. These regions are said to be peripheral, because they extend along the inlet and outlet faces, and where appropriate along the transverse faces of the amplifying plate.
  • a first heating electrode 232A covers a region of the upper face, respectively lower of the amplifying plate, on the side of the input face.
  • a second heating electrode 232A, respectively 232B covers a region of the upper face, respectively lower of the amplifier plate, on the side of the outlet face.
  • the upper, respectively lower, face of the amplifying plate is directly covered by a layer with a low optical index 220A, respectively 220B, called the low index layer, itself covered directly by the temperature control system 230A, respectively 230B.
  • Each low index layer 220A, 220B has an optical index lower than the average optical index of the amplifying plate (whether optical pumping is implemented or not, the index gradients then formed in the amplifying plate being much lower than the index difference with the low index layer).
  • the low index layers 220A, 220B are for example made of sapphire, deposited in the form of a thin layer of thickness to be chosen.
  • the temperature control system 230A, 230B rests directly on the upper, respectively lower, face of the amplifying plate.
  • the temperature control system 230A and the temperature control system 230B are symmetrical, or substantially symmetrical one of the other, according to an orthogonal symmetry relative to a plane P passing through the amplifying plate.
  • the plane P passes through the center of the amplifying plate.
  • the plane P extends parallel to the upper and lower faces of the amplifying plate, defined by the axes (y) and (z) of the reference (xyz).
  • the symmetry may not be perfect, in particular due to the angle of inclination of the pumping face.
  • a recovery rate between the temperature control system 230A, respectively 230B, and its symmetrical relative to the plane P is greater than 90%, and even greater than 95% or even 98%.
  • each temperature control system 230A, 230B has dimensions that are substantially invariant by a rotation of 180 ° around an axis ⁇ orthogonal to the upper and lower faces of the amplifying plate.
  • a recovery rate between each temperature control system 230A, 230B, and this same temperature control system turned 180 ° around the axis ⁇ is greater than 90%, and even greater than 95 % or even 98%.
  • this recovery rate is 100%.
  • the amplification device according to the invention is suitable for propagation of the laser beam 300 to be amplified, according to one or more propagations in a straight line in the amplifying plate, directly between the entry face and the exit face of the amplifying plate , without intermediate reflection (s) on another face of the amplifier plate.
  • the amplification device according to the invention is suitable for propagation of the laser beam to be amplified, along an axis substantially orthogonal to the entry face and / or the exit face of the amplifying plate (within a few degrees , for example +/- 2 °), for example along the axis (z).
  • the cooling elements 231A, 231B make it possible to cool the amplifying plate 210, preferably symmetrically by a rotation of 180 ° around the axis ⁇ .
  • the cooling elements 231A, 231B make it possible to maintain the average temperature of the amplifying plate below approximately 450 K.
  • the cooling elements 231A, 231B and heating electrodes 232A, 232B when activated, make it possible to modify the shape of the isothermal surfaces in the amplifying plate.
  • the degradation of the wave surface of the amplified laser beam is then very greatly reduced or canceled, even in the case of an amplifying plate thickness sufficiently high to leave room for the development of high local gradients.
  • these local gradients can be shaped so that they do not degrade the wave surface of the laser beam to be amplified, or even at least partially correct the thermo-mechanical deformation of the input and output faces of the amplifier plate.
  • the invention makes it possible to locally control the shape of the temperature gradients internal to the amplifying plate, and to compensate for the temperature differences which develop there, according to each dimension of the plate.
  • the invention thus makes it possible to propagate the wave surface of the amplified laser beam, without deforming it, through the amplifying plate, and despite a large plate thickness.
  • the invention makes it possible to use amplifying plates of high thickness, in particular between 3 mm and 10 mm, while obtaining a minimum deformation of the wave surface of the amplified laser beam.
  • the invention is implemented in combination with a propagation in a straight line of the laser beam to be amplified, in the amplifying plate, between the entry face and the exit face. This also makes it possible to eliminate the defects linked to multiple reflections on the cooled upper and lower faces, as described in the introduction and with reference to the figure 1 .
  • the cooling elements and heating electrodes can be configured together so that in operation, when the laser beam to be amplified propagates in a straight line in the amplifying plate, making one or more passages between the input face and the output face, the average temperature of the points of the amplifying plate, integrated along the axis of propagation of the laser beam to be amplified in the amplifying plate, is constant over the entire wave surface of this beam.
  • the temperature control systems can make it possible to completely correct the effect of the thermo-optical lens, corresponding to the thermo-optical effects naturally induced in the amplifying plate.
  • they can be configured together so that the average temperature of the points of the amplifying plate, integrated along the axis of propagation of the laser beam to be amplified in the amplifying plate, corresponds to an average optical index of the points of the amplifying plate, which, integrated along the same axis and for each point of the wave surface of the laser beam to be amplified, corresponds to a thermo-optical lens of known shape.
  • thermo-mechanical deformation of the inlet and outlet faces can make it possible to correct at least part of the effect of thermo-mechanical deformation of the inlet and outlet faces.
  • the temperature distribution allows each point on the wave surface to have a controlled optical path difference between the input and the output of the amplifying plate, which fully compensates for the thermo-optical and thermo-mechanical effects. in the amplifier plate.
  • the amplification device according to the invention does not include an external pre-compensation lens.
  • the temperature distribution allows each point on the wave surface to travel a controlled optical path between the input and the output of the amplifying plate, which fully compensates for the thermo-optical effects and partially the thermo-optical effects.
  • mechanical in the amplifier plate One or more external lens (s) for pre-compensation then compensates (s) for the uncorrected residual effect of the thermomechanical deformation.
  • the amplification device according to the invention can be configured to be crossed several times by the laser beam to be amplified, the optical path and the integration according to (z) then being considered on the sum of the several traverses of the laser beam to be amplified, from a first entry into the amplifying plate to a last exit out of the amplifying plate.
  • the amplification device according to the invention possibly including one or more external lens (s) for pre-compensation, can be configured so that a laser beam with incident amplifier, having a plane wave surface, presents at the output of the amplification device according to the invention a substantially plane wave surface, associated with a thermal lens with the highest possible focal length.
  • the laser beam to be amplified makes a single pass through the amplifying plate, propagating along the axis (z).
  • thermo-mechanical effect is corrected by an external lens called pre-compensation, not shown in figure 2 .
  • each point of the wave surface of the amplified laser beam has propagated parallel to the axis (z), passing, during the crossing of the amplifying plate, through a whole series of points aligned along axis (z), series of points to which a given average temperature can be associated.
  • This average temperature fixes the optical path traveled by the point considered of the wave surface of the amplified beam.
  • the temperature control systems are then dimensioned so that said average temperature is the same for each point of the wave surface of the amplified laser beam.
  • each point of the surface (xy) propagates in the plate according to a series of points aligned along the axis (z).
  • An average temperature can be associated with this series of points, which is defined at the end of the propagation in the amplifying plate.
  • the temperature control systems can be dimensioned so that each point on said surface is associated with the same average temperature.
  • the cooling elements cool the amplifying plate near its upper and lower faces, by forming cold zones 301A, 301B situated at the level of a central region of the upper face, respectively lower (see figure 3 ).
  • the heating elements make it possible to form in the amplifying plate, on either side of each of these cold zones 301A, 301B, hot zones 302A, 302B situated at the level of peripheral regions of the upper, respectively lower, face of the plate. amplifier (see figure 3 ).
  • thermo-optical effect produced by the cooling combined with optical pumping It is thus possible to compensate, using the heating elements, for the thermo-optical effect produced by the cooling combined with optical pumping.
  • the effect of the cold zones formed by the cooling elements is compensated by hot zones formed on either side of each cold zone by the heating elements.
  • the average temperature along an optical path parallel to (z) and passing through the center of the amplifier plate can then be substantially equal to the average temperature along an optical path parallel to (z) and passing through an edge of the amplifier plate.
  • each point of the wave surface travels the same length of optical path between the entry (just after entering the plate) and the exit of the amplifying plate (just before leaving the plate), so that 'a wave surface is not deformed during the crossing of the amplifier plate (excluding deformations linked to thermo-mechanical deformations of the input and output faces).
  • optical path difference or OPD, for English “ Optical Path Difference ”
  • the activation of the temperature control systems can in particular make it possible to flatten the isothermal surfaces, which then extend parallel to the plane (xy), to improve the optical quality of the laser beam to be amplified.
  • FIG 2 there is shown the particular case of an amplifier plate pumped by diodes in a transverse configuration, the pumping beam being oriented transversely, preferably orthogonal, relative to the direction of propagation of the beam. laser to be amplified.
  • the pumping beam is injected by a single side face of the amplifying plate.
  • pumping beams can be injected by several lateral faces of the amplifying plate, in particular two opposite lateral faces, in particular the two transverse faces as described above.
  • the pump beam can be injected through the entry face and / or the exit face, preferably inclined relative to the laser beam to be amplified.
  • the invention is therefore preferably associated with a transverse configuration, but can also be applied to a longitudinal pumping geometry.
  • the amplification device according to the invention is suitable for propagation of the laser beam 300 to be amplified, according to one or more propagations in a straight line in the amplifying plate.
  • the amplification device can comprise means for locating in space, to guide the positioning of a laser source emitting the laser beam to be amplified so that the laser beam to be amplified propagates in a straight line in the amplifier plate.
  • These locating means may include elements such as a test pattern or an inscription on a mechanical housing receiving the amplification device.
  • Such means are well known in the field of laser amplifiers, to help optimal centering and pointing of a laser beam.
  • FIGS. 4A to 4E illustrate different examples of geometries of a temperature control system according to the invention.
  • Each geometry is characterized by the shape of the cooling element, the shape of the heating electrode (s), and by their respective dimensions.
  • each electrode has the shape of a cylinder whose generator is parallel to the axis (x), and whose base extends parallel to the plane (yz), that is to say parallel on the upper and lower faces of the amplifier plate.
  • the temperature control system consists of a cooling element 431 1 , in the shape of a rectangular parallelepiped, which extends over the entire width of the amplifying plate.
  • Each electrode On either side of the cooling element 431 1 along the axis (z), extend two electrodes 432 1 symmetrical to one another.
  • Each electrode has the shape of a rectangular parallelepiped, extending over the entire width of the amplifying plate.
  • Each cooling element 431 1 and each electrode 432 1 has invariant dimensions along the axis (y).
  • the following configurations are not uniform along the axis (y), in particular to take into account the heat exchanges which take place at the level of the transverse faces. of the amplifier plate, and / or a non-uniform spatial distribution of the pump power along the axis (y).
  • the cooling element 431 2 has a shape of a rectangular parallelepiped, uniform along the axis (y), which extends over the entire width of the amplifying plate, and over more than half of its length.
  • the electrodes 432 2 differ from the electrodes of the figure 4A in that their respective faces, located facing the cooling element (parallel to the axis (x), therefore orthogonal to the upper and lower faces of the amplifying plate), are of rounded shape. In other words, these faces extend parallel to the axis (x), and have a curvature defined in planes orthogonal to the axis (x).
  • This rounded shape is a curved shape towards the inside of the amplifying plate, to take account of the presence of warmer areas which are more difficult to cool, at the geometric center of said plate.
  • the electrodes extend more or less deeply along the axis (z), depending on the position considered along the axis (y).
  • the cooling element 431 3 differs from the cooling element of the figure 4B in that its faces located opposite an electrode (parallel to the axis (x)) are of rounded shape.
  • These rounded shapes are shapes curved towards the outside of the amplifying plate, to compensate even more for the effects of the presence of warmer zones at the geometric center of said plate.
  • the electrodes 432 3 also each have a curved face towards the cooling element.
  • the cooling element 431 4 has the shape of a rectangular parallelepiped, which extends over only part of the width of the amplifying plate, and over more than half of its length.
  • the electrode (s) 432 4 completely surround (s) the cooling element 431 4 , along the inlet face, the outlet face, and the two transverse faces of the plate amplifier (not shown). It may be a single electrode, formed in one piece, or an array of electrodes.
  • the faces of the electrode (s) 432 4 located facing the cooling element, are curved towards the cooling element, for greater heating efficiency around a plane (xz) passing through the center of the amplifier plate.
  • the cooling element 431 5 has the shape of a cylinder with an oval base, surrounded by an electrode 432 5 in the shape of a rectangular parallelepiped pierced by an oval opening.
  • the shape of the electrodes can be adjusted according to the desired effect, the electrodes having a symmetry.
  • the optimal geometry of the cooling elements and the heating electrodes depends on the distribution of the total thermal load dissipated in the amplifier plate by the pump beam, and on the value of this thermal load.
  • the search for the optimal geometry generally corresponds to the search for a global thermal lens, associated with the amplification device in operation, having a focal length as long as possible.
  • the cooling elements can have different sections in a plane parallel to the plane (yz).
  • FIG. 4A to 4E presents a symmetry, in particular an invariance by a rotation of 180 ° around an axis (x).
  • Non-symmetrical variants are also possible, for example to take account of non symmetrical pumping power deposition distributions (which vary for example as one moves away from the injection face of the pump power).
  • the orthogonal symmetry relative to the plane P is not necessarily perfect, for example to take account of distributions of the deposition of pumping power that are not perfectly symmetrical.
  • cooling elements and the heating elements can have various shapes.
  • each heating element can cover a fraction of between 10% and 50% of the total surface of the upper face, respectively of the amplifying plate.
  • each temperature control system of an amplification device can be chosen as a function of parameters such as the pumping power, and the material constituting the amplifying plate.
  • the invention may include a method of adjusting the shape of the heating elements and the shape of the cooling elements, in order to optimize the efficiency of compensation for deformations of the wave surface of the laser beam to be amplified.
  • the figure 5A illustrates a temperature control system using the geometry of the figure 4D .
  • the figure 5B illustrates, from a top view, a distribution of the temperatures obtained in the amplifying plate, using the temperature control systems of the figure 5A .
  • the isothermal surfaces located at the periphery of the plate are shown in dotted lines, when the temperature control system is in operation and when the optical pumping of the laser beam to be amplified is implemented.
  • the electrical power supplied to the electrodes under the conditions considered is 5 W, and a total uniform thermal load of 20 W is dissipated in the amplifying plate, under the effect of optical pumping.
  • the temperature control system of the figure 6A differs from that of the figure 5A in that the electrodes 632 1 do not have curved faces towards the cooling element 631 1 (straight shapes in a plane (yz)).
  • the figure 6B illustrates the corresponding results.
  • the isothermal surfaces have strongly rounded shapes, which do not extend parallel to one another and are not parallel to the plane (xy).
  • the shape and the section of the heating elements and cooling elements form parameters for adjusting the distribution of the temperature gradients in the amplifying plate.
  • the optimal geometry can be selected by simulating temperatures in the amplifier plate and resulting deformation of the wave surface of the laser beam after amplification.
  • an optimal heating power is also defined to be generated by means of the heating elements.
  • the shape of the wave surface of an amplified laser beam has been represented, after passing through an amplifying plate as described in the device of the figure 2 , for a thickness and a width of respective values 5 mm and 20 mm, and for example for an electrical power of 2 W supplied to the electrodes.
  • Figures 7A and 7B are graduated in arbitrary units, according to the vertical plane (xy) of the previous figures, and contain the two dimensions fixed by the width and the thickness of the plate.
  • the ordinate axis is that along which the optical path difference (OPD) is represented, in ⁇ m, along the axis (z) of the preceding figures.
  • OPD optical path difference
  • the peak-to-peak difference in optical path, along the ordinate axis of the figure 7A is worth approximately 1.7 ⁇ m after amplification under the conditions described here.
  • the electric power supplied to the electrodes is reduced to 1.3 W.
  • the corresponding peak-to-peak difference in optical path is then reduced by a factor of around 4, after amplification, to a level also much lower than that naturally generated in the plate before activating the heating electrodes.
  • the abscissa axis is an electric power supplied to the electrodes, expressed in W
  • the ordinate axis is the quadratic mean of the optical path difference characterizing the deformation of the wave surface, at the output of the amplifying plate .
  • the figure 7C shows that the heating power dissipated by the heating electrodes constitutes an optimum adjustment parameter for the quality of the amplified beam.
  • the figure 7C also shows the existence of an optimal value of the thermal heating power, associated with a minimum distortion of the wave surface after amplification.
  • the figure 8 thus illustrates a second embodiment of a laser amplification device 800 according to the invention, according to a perspective view, for the automation of the adjustment of the optimal electrical power to be supplied to each heating electrode.
  • This second embodiment will only be described for its differences relative to the embodiment of the figure 2 .
  • the heating electrodes 832A and 832B are connected to electrical supply means 855, configured to supply electrical supply power to each heating electrode.
  • These electrical supply means 855 are adjustable, the electrical power which they supply to each heating electrode being a function of a control instruction which they receive.
  • Each electrode can be supplied with a different value of electric power.
  • the piloting instruction is supplied by piloting means 854, for example a processor. It is formulated taking into account the result of a comparison between a maximum wave surface deformation setpoint, and a measurement of the wave surface of the amplified laser beam, at the output of the amplifying plate.
  • the comparison is implemented by a comparator 853, receiving as input the setpoint 852 of maximum deformation, and the measurement of the wave surface.
  • the maximum deformation setpoint 852 is a fixed value stored in a memory.
  • the wave surface measurement is provided by wave surface measurement means 851. It is implemented on the amplified laser beam, in particular on a sample thereof, taken for example using a partially reflecting mirror.
  • control setpoint is adapted to maintain the wave surface deformation of the amplified laser beam at a minimum value.
  • the figure 9A illustrates a third embodiment of a laser amplification device 900 according to the invention, according to a perspective view.
  • This third mode illustrates an external pre-compensation lens, as mentioned above.
  • This third embodiment associating the amplifying plate with an external lens for pre-compensating for the distortions of the wave surface, is the one which allows the greatest finesse of control with a view to an almost total cancellation of the surface deformations. wave after amplification.
  • an external lens 960 extends at the inlet or at the outlet of the amplifying plate, over the entire extent of one of its inlet faces or output, to compensate for at least some of the thermal effects generated in the amplifier plate by optical pumping.
  • It is preferably a plane-cylinder lens, generally plano-concave (type of lens mainly related to the coefficient of thermal expansion of the material of the amplifying plate).
  • thermal effects include the thermo-optical effects linked to temperature distributions in the amplifying plate, and the thermo-mechanical effects corresponding to the mechanical deformation of the entry and exit faces of the amplifying plate under the action of heat. .
  • optical pumping in the amplifying plate results in the appearance of a mechanical deformation of the input face (respectively of the output) in its central zone, of a peak-to-peak value of 1.5 ⁇ m.
  • thermo-mechanical origin Preferably, most of the deformations of thermo-mechanical origin are corrected statically, by this external pre-compensation lens, lens whose focal length is then of opposite sign to that of thermo-mechanical origin.
  • This external pre-compensation lens lens whose focal length is then of opposite sign to that of thermo-mechanical origin.
  • the role of temperature control systems essentially becomes that of compensation for thermo-optical effects in the amplifier plate.
  • the external pre-compensation lens 960 is not necessary, the temperature control systems being able to fully correct the thermo-optical lens and the thermo-lens. mechanical induced by optical pumping in the amplifier plate.
  • the figure 9B illustrates the laser amplification device 900 according to a sectional view in a plane parallel to (xz). For reasons of readability, the thickness of the amplifying plate is exaggerated.
  • the wave surface of the laser beam being amplified is shown in dotted lines, at different stages of the propagation of said laser beam inside the amplifying plate.
  • the temperature control systems 930A, 930B are actuated, forming inside the amplifier plate cooled regions 971A, 971B, under the cooling elements, and heated regions 972A, 972B, under the heating electrodes.
  • the optical pumping is activated, forming a heated region 970 at the center of the amplifying plate.
  • the wave surface of the laser beam to be amplified is assumed to be plane. It undergoes an initial deformation linked to the mechanical deformation of the input face 911, then a first series of deformations during its propagation from the input face 911, to the center of the amplifying plate. It then undergoes a second series of deformations during propagation from the center of the amplifying plate to the exit face 912, substantially symmetrical to the first series of deformations, then a final exit deformation linked to the thermo-mechanical deformation of the output face 912.
  • the wave surface of the amplified laser beam then exhibits, at the output of the amplifying plate, a residual deformation, which is corrected by the lens 960.
  • this residual deformation is delimited in space by two aspherical shapes, or two cylindrical shapes, defining the shape of the spherical or cylindrical lens 960.
  • the wave surface of the amplified laser beam has, at the output of the amplifying plate, a residual deformation defined by two cylinders of orthogonal axes. This deformation is then compensated by two plane-cylinder lenses, the axes of the cylinders being orthogonal to each other and located in a plane (xy).
  • a complete laser amplification system 1000 according to the invention comprising a laser amplification device according to the invention 1100.
  • the system is shown schematically, according to a top view.
  • the system 1000 comprises a support 1080, or housing, configured to receive the laser source 1081 for emitting the laser beam to be amplified.
  • the support 1080 and the laser amplification device 1100 are positioned relative to each other, so that the laser beam to be amplified propagates in a straight line in the amplifying plate, directly from its entry face 1111 to at its exit face 1112, without intermediate reflection on the upper and lower faces.
  • the laser beam to be amplified propagates in particular in a direction orthogonal to the entry and exit faces (considered at rest, in the absence of thermomechanical deformation). This normal incidence minimizes the effect of any optical aberrations induced during propagation in the amplifying plate.
  • the laser source 1081 can be an integral part of the laser amplification system according to the invention.
  • the system 1000 comprises means described below, for implementing several passages of the laser beam to be amplified, through the amplifying plate and along its length.
  • the laser beam to be amplified propagates parallel to the same direction, at each of its passages through the amplifying plate.
  • the laser beam to be amplified is called the laser beam to be amplified, obtained after amplification by all of the passage (s) through the amplifying plate.
  • the laser beam to be amplified 300 emitted by the laser source 1081, p-polarized, passes through a polarization splitter blade 1091 inclined at the incidence which is suitable, generally 55 to 60 degrees, relative to the incident laser beam.
  • This polarization splitter plate 1091 transmits the polarization p and reflects the polarization s.
  • the laser beam to be amplified then goes to the laser amplification device 1100, at an incidence normal to the entry face 1111 of the amplifying plate.
  • roof mirror consisting of a pair of reflectors 1092 1 , 1092 2 arranged at 90 ° from one another, and each inclined at 45 ° (at + / - 2 ° near) relative to the entry face of the amplifier plate.
  • a second roof mirror made up of another pair of reflectors 1093 1 , 1093 2 .
  • Each of the reflectors 1092 1 , 1092 2 , 1093 1 , 1093 2 has its reflecting face on the side of the amplifying plate.
  • each of the reflectors 1092 1 , 1092 2 , 1093 1 , 1093 2 is inclined at 45 ° exactly relative to the input and output faces of the amplifying plate, to guarantee a normal incidence of the laser beam to be amplified, at each passage in said plate.
  • These four reflectors are configured together so that the laser beam to be amplified crosses the amplifying plate several times, propagating directly between the entry face and the exit face of said plate.
  • the laser beam to be amplified crosses the amplifying plate from side to side several times, shifting along the axis (y) between two crossings, by successive reflections on the reflectors 1092 1 , 1092 2 , 1093 1 , 1093 2 .
  • the reflectors 1092 1 , 1092 2 , 1093 1 , 1093 2 are arranged so that at each of these crossings, the laser beam to be amplified extends inside the amplifying plate according to a distinct volume.
  • these different volumes are not superimposed, but juxtaposed, and together occupy the entire volume of the amplifying plate.
  • the pump beam advantageously extends over the entire volume of the amplifying plate.
  • the objective is to maximize the spatial overlap between the absorption zone of the pump beam and the laser beam to be amplified.
  • the laser beam crosses a quarter-wave plate 1094, then is reflected on a reflector 1095.
  • the reflector 1095 is arranged orthogonal to the incident laser beam, so that it returns this laser beam on the same optical path.
  • the laser beam returning towards the amplifying plate has a polarization rotated by 90 °, ie a polarization s.
  • the reflector 1095 and the quarter-wave plate 1094 are configured together so that the laser beam to be amplified crosses the amplifying plate several times, having a first polarization, then having a second polarization.
  • the laser beam to be amplified thus makes 4 new crossings of the amplifying plate, this time with the polarization s.
  • the output At the output, it forms the so-called amplified laser beam, which propagates to the polarization splitter plate 1091, on which it is reflected.
  • the laser beam to be amplified is thus amplified in 8 successive passages through the amplifying plate.
  • the polarization splitter plate 1091, the reflectors 1092 1 , 1092 2 , 1093 1 , 1093 2 , the quarter wave plate 1094 and the reflector 1095 together form means for multiplexing the laser beam to be amplified. These means implement here a spatial multiplexing (the reflectors 1092 1 , 1092 2 , 1093 1 , 1093 2 ) and a polarization multiplexing (quarter wave plate 1094 and reflector 1095).
  • multiplexing means By abuse of language, these means are called “multiplexing means". However, it is obvious, on reading the text, that these means aim to multiply a number of passages in the amplifier plate, and not to separate a signal into several distinct signals.
  • spatial multiplexing designates the multiplication of a number of passages in the amplifying plate using spatial shifts of the laser beam.
  • the configuration illustrated in figure 10 gives access to gains of between 15 and 20 dB or even more, depending on the initial level of power or energy of the pulses of the laser beam to be amplified.
  • It can include a lens as described with reference to Figures 9A and 9B .
  • This example is that, the most typical and optimized with regard to the conditions of implementation of the invention, of an amplifier with multiple passages along the amplifier plate equipped with its cooling and heating elements.
  • the optical architecture proposed here makes it possible to make optimal use of the wave surface control functionalities.
  • These transmission means can be an integral part of the system according to the invention.
  • These emission means are configured here so that the pumping laser beam propagates along the axis (Oy), orthogonal to the direction of propagation of the laser beam to be amplified.
  • they can be configured so that the pumping laser beam propagates in another direction, by being injected by one or more lateral faces of the amplifying plate.
  • These transmission means are further configured so that the pump power is distributed in a substantially homogeneous manner, and preferably throughout the volume of the amplifying plate.
  • a pump panel consisting of stacks of bar-shaped diodes generally arranged in rows and columns.
  • Each diode contained in a stack is collimated along its fast axis.
  • a set of plane-cylinder lenses of large dimensions extending over the entire extent of the diode panel implements collimation, then focusing of all of the beams emitted by these diodes.
  • This optical pumping device provides the required brightness on the injection face of the pump in the amplifier plate.
  • an optical homogenizer installed on one or more blade (s) with little absorption (s), comprising a series of suitable patterns which can be in the form of micro-lenses, making it possible to avoid the presence of hot spots in the amplifier plate.
  • each heating element may consist of a plurality of electrodes which can each be turned on or off independently of the others, to dynamically adjust the form emitting heat, in operation.
  • the amplification device makes it possible to obtain laser pulses whose ranges of average power and energy per pulse are between a few tens of W and 1 kW, respectively between 10 mJ and 1J.
  • the invention makes it possible in particular to maintain a high amplification section for the production of high energies with a large amplification gain, while controlling the deformation of the wave surface of the amplified beam using a control of the spatial distribution of the thermal load generated in the plate.

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Claims (13)

  1. Laserverstärkungsvorrichtung (200; 800; 900; 1100), enthaltend eine Verstärkerplatte (210; 910) mit einer Eingangsseitenfläche (911; 111) und einer Ausgangsseitenfläche (212; 912; 1112) für einen zu verstärkenden Laserstrahl (300), deren Ober- und Unterseite jeweils mit einem Temperaturregelsystem (230A, 230B; 930A, 930B) überdeckt ist, dadurch gekennzeichnet, dass jedes Temperaturregelsystem (230A; 230B; 930A, 930B) ein Kühlelement (231A; 231B; 4311; 4312; 4313; 4314; 4315; 6311; 831A) enthält, das einen Mittelbereich der Ober- bzw. Unterseite der Verstärkerplatte überdeckt, sowie zumindest ein Heizelement (232A; 232B; 4321; 4322; 4323; 4324; 4325; 6321; 832A), das Umfangsbereiche der Ober- bzw. Unterseite der Verstärkerplatte überdeckt, und dass die Temperaturregelsysteme (230A; 230B; 930A; 930B) in einer Symmetrie orthogonal zur einer Ebene (P) im Wesentlichen symmetrisch zueinander sind, wobei die Ebene (P) eine Ebene ist, die parallel zu der Ober- und der Unterseite der Verstärkerplatte (210; 910) ist und durch die Platte verläuft, und wobei jedes Temperaturregelsystem eine Überdeckungsrate von mehr als 90% mit der Symmetrie des anderen Temperaturregelsystems aufweist.
  2. Vorrichtung (200; 800; 900; 1100) nach Anspruch 1, dadurch gekennzeichnet, dass jedes Temperaturregelsystem (230A; 230B; 930A; 930B) bei einer Drehung um 180° um eine Achse (Δ) orthogonal zur Oberseite der Verstärkerplatte (210; 910) im Wesentlichen unveränderlich ist, wobei jedes Temperaturregelsystem eine Überdeckungsrate von mehr als 90% mit demselben um 180° um diese Achse gedrehten Temperaturregelsystem aufweist.
  3. Vorrichtung (200; 800; 900; 1100) nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass die Dicke (E) der Verstärkerplatte (210; 910) größer oder gleich 3 mm ist.
  4. Vorrichtung nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass bei jedem Temperaturregelsystem das zumindest eine Heizelement (4322; 4323; 4324; 4325) abgerundete Seiten aufweist, die sich dem Kühlelement (4312; 4313; 4314; 4315) gegenüberliegend entlang einer Achse (x) orthogonal zur Ober- und Unterseite der Verstärkerplatte erstrecken.
  5. Vorrichtung nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, dass bei jedem Temperaturregelsystem das zumindest eine Heizelement (4324; 4325) das Kühlelement (4314; 4315) vollständig umgibt.
  6. Vorrichtung nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass bei jedem Temperaturregelsystem das Heizelement (4313; 4315) einen nicht rechteckigen Querschnitt in einer Ebene parallel zur Oberseite der Verstärkerplatte aufweist.
  7. Vorrichtung (900) nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass sie ferner zumindest eine äußere Linse (960) enthält, die sich am Eingang bzw. Ausgang der Verstärkerplatte (910) erstreckt und dazu ausgelegt ist, zumindest teilweise den Effekt einer thermomechanischen Verformung der Eingangs- und der Ausgangsseitenfläche der Verstärkerplatte auszugleichen.
  8. Vorrichtung (200; 800; 900; 1100) nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass die Ober- bzw. Unterseite der Verstärkerplatte (210; 910) direkt mit einer sogenannten Niederindex-Schicht (220A; 220B) überdeckt ist, deren optischer Index niedriger als der optische Mittelwertindex der Verstärkerplatte ist, wobei jede Niederindex-Schicht direkt mit dem entsprechenden Temperaturregelsystem überdeckt ist.
  9. Vorrichtung (800) nach einem der Ansprüche 1 bis 8, dadurch gekennzeichnet, dass bei jedem Temperaturregelsystem das zumindest eine Heizelement (832A; 832B) über einstellbare Versorgungsmittel (855) versorgt wird und dass die einstellbaren Versorgungsmittel mit Steuermitteln (854) verbunden sind, die dazu ausgelegt sind, eine Steuervorgabe in Abhängigkeit von dem Ergebnis eines Vergleichs zwischen einer maximalen Verformungsvorgabe der Wellenoberfläche und einer Messung der Wellenoberfläche an einem verstärkten Laserstrahl am Ausgang der Verstärkerplatte zu bilden.
  10. Vorrichtung (800) nach einem der Ansprüche 1 bis 9, dadurch gekennzeichnet, dass sie ferner Mittel zum Lokalisieren in Bezug auf die Verstärkerplatte enthält, die dazu ausgelegt sind, um die Positionierung des zu verstärkenden Laserstrahls (300) so zu führen, dass er sich in einer geraden Linie in der Verstärkerplatte ausbreitet.
  11. System (1000), enthaltend eine Vorrichtung (1100) nach einem der Ansprüche 1 bis 10, dadurch gekennzeichnet, dass es ferner Mittel zum Vervielfachen von Durchgängen enthält, die dazu ausgelegt sind, um eine Anzahl von Durchgängen des zu verstärkenden Laserstrahls in der Verstärkerplatte zu vervielfachen.
  12. System (1000) nach Anspruch 11, dadurch gekennzeichnet, dass die Mittel zum Vervielfachen von Durchgängen zwei Reflektoren (10921, 10922) enthalten, die auf der Seite der Eingangsseitenfläche der Verstärkerplatte angeordnet sind, sowie zwei Reflektoren (10931, 10932), die auf der Seite der Ausgangsseitenfläche der Verstärkerplatte angeordnet sind.
  13. System (1000) nach Anspruch 12, dadurch gekennzeichnet, dass die Mittel zum Vervielfachen von Durchgängen auch ein Viertelwellenplättchen (1094) und einen Reflektor (1095) enthalten, die dazu ausgelegt sind, eine Anzahl von Durchgängen des zu verstärkenden Laserstrahls in der Verstärkerplatte zu verdoppeln.
EP17711231.5A 2016-03-21 2017-03-21 Laserverstärkervorrichtung mit aktiver steuerung der strahlqualität Active EP3433910B1 (de)

Applications Claiming Priority (2)

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FR1652393A FR3049122B1 (fr) 2016-03-21 2016-03-21 Dispositif d'amplification laser a controle actif de la qualite de faisceau
PCT/EP2017/056615 WO2017162621A1 (fr) 2016-03-21 2017-03-21 Dispositif d'amplification laser à contrôle actif de la qualité de faisceau

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EP3433910B1 true EP3433910B1 (de) 2019-12-18

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EP3309913A1 (de) * 2016-10-17 2018-04-18 Universität Stuttgart Strahlungsfeldverstärkersystem

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JPH05226732A (ja) * 1992-02-12 1993-09-03 Hitachi Ltd スラブレーザ装置とその熱レンズ効果抑制方法及びレーザ加工装置
US6034977A (en) * 1998-02-17 2000-03-07 Trw Inc. Optical path difference control system and method for solid state lasers
US6134258A (en) * 1998-03-25 2000-10-17 The Board Of Trustees Of The Leland Stanford Junior University Transverse-pumped sLAB laser/amplifier
US7170919B2 (en) * 2003-06-23 2007-01-30 Northrop Grumman Corporation Diode-pumped solid-state laser gain module
US7280571B2 (en) * 2004-11-23 2007-10-09 Northrop Grumman Corporation Scalable zig-zag laser amplifier

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FR3049122A1 (fr) 2017-09-22
FR3049122B1 (fr) 2018-07-06
EP3433910A1 (de) 2019-01-30
WO2017162621A1 (fr) 2017-09-28

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